The invention in general relates to acoustic transducers and more particularly to an acoustic transducer of predetermined acoustic characteristics.
The active element of an acoustic transducer generally comprises a piezoelectric member having connected thereto electrical leads. Such active element can be given precise characteristics with regard to transmission and/or reception of acoustical waves. However, due to size and fragility the piezoelectric member must be embodied within a transducer assembly to form a protected unitary device which can be used, mounted or positioned as part of a practical acoustic equipment, for instance in a flowmeter.
The problem with the transducer assemblies of the prior art is to keep the good electrical and acoustical qualities of the components, and to be able to obtain a unitary device which can be manufactured easily, at minimum cost and with good reproducibility.
It is known from U.S. Pat. No. 3,771,117 of T. N. Shaffer et al., a patent assigned to the same assignee as the assignee of this application, to mount a transducer assembly within a holder, or casing, having a closed end and an open end, the closed end serving as an acoustic window for the transducer assembly, and to position the transducer assembly with force within the holder against the inside surface of such acoustic window. In order to obtain a tighter and more unitary transducer assembly, the above patent of Shaffer proposes to use an encapsulating elastomeric material surrounding the active element and held by a backing organ against the assembly holder and contained therein.
While the arrangement of the Shaffer patent is well suited for the particular conditions of applications defined therein, the present invention aims at providing a more integrated type of transducer, without the need for any springs to hold the transducer assembly in effective operative condition within the holder, and which comes as a unit with the casing itself. In addition, such unitary encapsulated transducer assembly must have predetermined acoustic characteristics and be capable of being reproduced by a manufacturing process with identical acoustic characteristics and the same overall quality.